The energy in moving air has been used for millennia, with applications ranging from sailing ships to pumping fresh water for agricultural irrigation. The first application of wind power for generating electricity has variously been attributed to Prof. James Blyth of Anderson's College in Glasgow, who in 1887 developed a 33-foot-tall wind turbine, and to Charles F. Brush who established the Brush Electric Company in 1880, and in 1888 designed and built a 60-foot-tall wind turbine.
Wind power generation capacity has grown dramatically in recent years, pursuing the twin goals of clean energy generation and energy independence. The U.S. Energy Information Administration reports that wind energy production in the U.S. increased from about 14 terawatt-hours in 2004 to about 168 terawatt-hours in 2013. Currently, wind power is the second largest source of renewable energy produced in the United States, second only to hydroelectric power.
Wind turbine design has evolved towards larger turbines to enable generating greater amounts of electrical power from each installation. Advances in blade design and materials have enabled increasingly larger wind turbine blades to capture more wind energy. In June 2011, Sandia National Laboratories issued a report on a study directed to a 100-meter wind turbine blade design, “The Sandia 100-meter All-glass Baseline Wind Turbine Blade: SNL100-00,” T. D. Griffith and T. D. Ashwill, Tech. Rep., Sandia National Laboratories, Albuquerque, N. Mex. (2011), which is hereby incorporated by reference.
Modern wind turbine blades are typically constructed substantially from composite materials, e.g., fiber-reinforced plastics (FRPs). Suitable composite materials include, for example, glass or carbon fibers embedded in a resin matrix. In a conventional blade, the majority of the fibers are oriented longitudinally, along the span of the blade, so the fibers can best resist the primary bending loads on the blade during operation.
In U.S. Patent Application Publication 2013/0236327, titled “Advanced Aerodynamic and Structural Blade and Wing Design,” which is hereby incorporated by reference in its entirety, one of the present inventors (Wirz) discloses a new class of blades for wind turbines that improves the structural and aerodynamic performance of the inboard region the blade. In particular, the new turbine blade includes an inboard biplane portion and an outboard monoplane portion. The pair of slender airfoils that define the biplane portion improve aerodynamic performance in the inboard region of the blade, thereby increasing the overall efficiency of the blade. In addition, the biplane airfoils are spaced apart, providing a large bending moment of inertia in the inboard region, thereby improving the blade tip deflection characteristics. Ultimately, the hybrid biplane/monoplane blade enables longer turbine blades, resulting in increased power production capabilities.
One goal of the present invention is to provide a novel construction for a hybrid turbine blade having an inboard multi-plane (e.g., biplane) portion and an outboard monoplane portion.
When designing a monoplane blade, the conventional practice is to first design an external airfoil profile based primarily on aerodynamic considerations. Then a suitable support structure is designed to fit within the blade envelope. However, this conventional method is not suited for designing hybrid multi-element turbine blades. The present application, therefore, also discloses a new “inside-out” design method for designing a hybrid blade wherein a spar structure is first designed, and then suitable airfoil profiles are fitted over the spar structure.
It is contemplated that the disclosure herein can also be applied and extended to other multi-element airfoil structures, including, for example, blades incorporating regions defining triplane or quadplane portions. The hybrid blade structures disclosed herein can also be modified for use in fluid pumps, propellers, and other similar devices.